Robotic arms

Abstract

A robotic arm comprises a plurality of articulated elements, and control means for controlling the position of various of the elements such that the arm may adopt serpentine shape for tip following movement. Means for measuring directly the relative positions of at least some of the elements are provided in order to calculate deviation from the theoretical shape, and apply corrections to the arm control means.

What is claimed is: 
     
       1. A robotic arm comprising at least one segment having a plurality of articulated elements, comprising a control element and at least one passive element, a controller for controlling the position of the arm by acting on the control element of each segment, and a measuring device associated with the controller and arranged to measure the relative position of at least one element in each segment with respect to at least one other element in the arm for determining the actual shape of the arm, in which the measuring device is arranged to measure the relative position of at least one pair of adjacent elements in each segment. 
     
     
       2. The robotic arm as claimed in  claim 1 , comprising a calculating unit associated with the controller and the measuring device for calculating a difference between the actual shape of the arm and a predetermined shape, and for applying a correction to the controller corresponding to the difference. 
     
     
       3. The robotic arm as claimed in  claim 1 , in which the measuring device is arranged to measure the angular relationship between the transverse planes of the elements. 
     
     
       4. The robotic arm as claimed in  claim 1 , in which the measuring device is arranged to measure the relative pose of the elements. 
     
     
       5. The robotic arm as claimed in  claim 1 , in which the measuring device comprises an energy generator for generating an energy beam carried by one element in the pair of adjacent elements, and an array of energy sensors carried by the other element in the pair of adjacent elements, adapted to sense the energy beam. 
     
     
       6. The robotic arm as claimed in  claim 5 , in which the energy beam is electromagnetic energy, preferably light, and the sensors comprise an elongate array of sensors that extend along an expected path of movement of the beam. 
     
     
       7. The robotic arm as claimed in  claim 5 , in which the measuring device comprises a plurality of spaced pairs of the said generators and sensors. 
     
     
       8. The robotic arm as claimed in  claim 1 , in which the measuring device is arranged to measure the distance between adjacent elements at a plurality of spaced positions. 
     
     
       9. The robotic arm as claimed in  claim 8 , in which the measuring device comprises a plurality of linear potentiometers mounted between the elements at or adjacent the periphery thereof. 
     
     
       10. A robotic arm comprising at least one segment having a plurality of articulated elements, comprising a control element and at least one passive element, a controller for controlling the position of the arm by acting on the control element of each segment, and a measuring device associated with the controller and arranged to measure the relative position of at least one element in each segment with respect to at least one other element in the arm for determining the actual shape of the arm, in which the controller comprises at least one group of control wires attached to an associated control element, each control wire having an actuator for altering the length of the wire, and in which the measuring device comprises a wire displacement measuring device arranged to measure directly the length of each control wire. 
     
     
       11. The robotic arm as claimed in  claim 10 , in which the wire displacement measuring device comprises a pair of pinch rollers disposed one on either side of each wire, and a sensor arranged to sense the angular displacement of at least one of the rollers. 
     
     
       12. The robotic arm as claimed in  claim 10 , in which the wire displacement measuring device comprises a sensor for sensing the position of at least one marker of the wire. 
     
     
       13. A robotic arm comprising at least one segment having a plurality of articulated elements, comprising a control element and at least one passive element, a controller for controlling the position of the arm by acting on the control element of each segment, and a measuring device associated with the controller and arranged to measure the relative position of at least one element in each segment with respect to at least one other element in the arm for determining the actual shape of the arm, in which the measuring device comprise a wire displacement measuring device arranged to measure the displacement of a group of measuring wires associated with each element the position of which is measured. 
     
     
       14. The robotic arm as claimed in  claim 13 , in which the wire displacement measuring device comprises optical or magnetic sensors. 
     
     
       15. The robotic arm as claimed in  claim 13 , in which the wire displacement measuring device comprises a sensor for sensing the position of at least one marker of the wire. 
     
     
       16. A method of operating a robotic arm, the arm comprising at least one segment having a plurality of articulated elements, comprising a control element and at least one passive element, the method comprising:
 controlling the position of the control element in each segment; 
 measuring the relative position of at least one pair of adjacent elements in each segment; 
 calculating a difference between the relative position measured and a predetermined position; and 
 applying a correction to compensate for the difference.